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openresolv is aresolvconfimplementation which manages/etc/resolv.conf.

/etc/resolv.conf is a file that holds the configuration for the localresolution of domain names.Normally this file is either static or maintained by a local daemon,normally a DHCP daemon. But what happens if more than one thing wants tocontrol the file?Say you have wired and wireless interfaces to different subnets and run a VPNor two on top of that, how do you say which one controls the file?It's also not as easy as just adding and removing the nameservers each clientknows about as different clients could add the same nameservers.

Enter resolvconf, the middleman between the network configuration services and/etc/resolv.conf.resolvconf itself is just a script that stores, removes and lists a fullresolv.conf generated for the interface. It then calls all the helper scriptsit knows about so it can configure the real/etc/resolv.conf and optionallyany local nameservers other than libc.

Why openresolv over theDebian implementation?Here's some reasons:

• Works withPOSIX shell and userland
• Does not need awk, grep or sed which means we can work without/usrmounted
• Works with other init systems than Debians' out of the box
• Available as a 2 clauseBSD license
• Prefer configs via IF_METRIC for dynamic ordering
• Configures zones for local resolvers other than libc

The last point is quite important, especially when running VPN systems.Take the following resolv.conf files which have been generated by aDHCP client and sent to resolvconf:

# resolv.conf from bge0search foo.comnameserver 1.2.3.4# resolv.conf from tap0domain bar.orgnameserver 5.6.7.8

In this instance, queries for foo.com will go to 1.2.3.4 and queries forbar.org will go to 5.6.7.8.This does require the resolvers to be configured to pickup the resolvconfgenerated configuration for them though.openresolv ships with helpers for:

• unbound
• dnsmasq
• ISC BIND
• PowerDNS Recursor
• systemd-resolved

See theconfiguration sectionfor more details.

If openresolv updates/etc/resolv.conf it can notify the following of this:

• Bonjour (mdnsd)
• avahi